A US soldier takes part in house-to-house searches during the November 2004 assault on the Iraqi town of Falluja Photograph: Scott Peterson/Getty Images

SAS troops were prevented from joining an American assault on the Iraqi town of Falluja because British commanders strongly disapproved of US military tactics, it has been revealed.

Falluja, a stronghold of the Sunni insurgency, was the target of a fierce attack by US forces in the spring of 2004. Despite the fact that the bombing led to huge civilian casualties and gave the insurgency a propaganda gift, US commanders planned a fresh onslaught on the city in November of the same year.

British defence chiefs were worried about the impact of US tactics on both the Sunni insurgency, backed by al-Qaida, and increasing Shia militancy in southern Iraq, where most British soldiers were based. They believed the US tactics were counterproductive.

So concerned were they that they vetoed plans for the SAS to take part in the November assault, the author and journalist Mark Urban discloses in his book Task Force Black, which is published on Thursday.

"Orders came down from the chain of command that they [the SAS] were not to do so. Britain had played another red card in a national caveat," he writes.

It is known that Tony Blair had already personally expressed the concerns of British military commanders about US tactics in the first assault on Falluja at a meeting with President George Bush in the US in April 2004.

Urban also says that MI6 was so concerned about conditions at a secret US detention centre at Balad, north of Baghdad, that SAS soldiers were told to hand over prisoners to American forces only if the US undertook not to send them there.

John Hutton, the then defence secretary, admitted to MPs last year that in 2004 UK forces in Iraq handed over individuals to their US counterparts, who subsequently flew them to a secret prison in Afghanistan. He referred to allegations by Ben Griffin, a former SAS soldier, that prisoners handed over by British special forces had ended up in secret prisons in breach of the Geneva conventions and international law.

Griffin alleged that Iraqis and Afghans were captured by British and US special forces and rendered to prisons where they faced torture. The MoD obtained a gagging order to prevent Griffin from saying anything further.

Urban's book is the latest to drive a coach and horses through the official line that nothing should be published about any British special forces operations. This remains official policy even though special forces are playing an increasingly significant role in military operations, including in Afghanistan.

Urban says in his preface that the MoD objected to certain passages in his book. He agreed to some changes, though he says many were "essentially pointless".

He says that during six years in Iraq the task force of 150 killed or captured 3,500 people. Most were captured, with the number killed probably ranging between 350 and 400.